Real-time Applications with Socket.IO and Node.js

Introduction to WebSockets and Socket.IO

WebSockets provide full-duplex communication over a single TCP connection. Socket.IO adds reconnection, fallbacks, and room support on top of the WebSocket API, making it easier to build chat apps, live dashboards, and collaborative tools.

Setting Up a Socket.IO Server

Attach Socket.IO to your existing HTTP server (Express, Fastify, or the built-in http module). Use namespaces to separate concerns (e.g. /chat, /notifications) and middleware for authentication and validation.

const { createServer } = require('http');
const { Server } = require('socket.io');
const server = createServer(app);
const io = new Server(server, { cors: { origin: '*' } });
io.on('connection', (socket) => {
  console.log('Client connected:', socket.id);
});

Rooms and Broadcasting

Rooms let you group sockets (e.g. by channel or user). Use socket.join(roomId) and then io.to(roomId).emit('event', data) to broadcast to that room. Private messaging can be implemented with rooms per conversation.

Scaling in Production

For multiple server instances, use the Socket.IO Redis adapter so that events are broadcast across nodes. Implement sticky sessions or ensure your load balancer supports WebSocket upgrade. Monitor connection count and message throughput.